1. Field of the Invention
The present invention relates to a method of making nanosized metal compounds, and in particular, to a method of making nanosized copper and copper compounds useful as catalysts and pigments.
2. Description of Related Art
Nanometer sized particles have diameters in the range from about 1 nanometer (10−9 meter) to about 100 nanometers (10−7 meter). These materials are also described in the art as nanostructured, nanocrystalline, nanosized, nanoparticulate, nanoscale, ultrafine or superfine. Their structures and high surface to volume ratio make them desirable in catalytic, electronic, magnetic and coating (pigment) applications. Various physical and chemical methods have been disclosed in the prior art for their preparation.
Jia et al., Chinese Science Bulletin, 43, (1998), pp. 571–74, reported the synthesis of nanosized copper (II) oxide, CuO, by grinding a 1:2 molar mixture of CuCl2.2H2O and NaOH in a mortar at room temperature. The CuO particles averaged 23 nanometers in diameter. However, this one step solid state reaction was not successful with Cu(OH)2 as the starting material.
Dhas et al., Chemistry of Materials, 10, (1998), pp. 1446–52, prepared nanosized copper and copper (I) oxide by the thermal and sonochemical reduction of copper (II) hydrazine carboxylate in an aqueous medium. Thermal reduction produced irregularly shaped copper particles with dimensions of 200 to 250 nanometers. A mixture of metallic copper and copper (I) oxide was obtained by sonochemical reduction. The solid consisted of 50 to 70 nanometer aggregates of smaller nanosized particles.
Pileni, M. P., J. Physical Chemistry, 97, (1993), pp. 6961–73, reviewed the synthesis of nanosized copper and copper compounds in reverse microemulsions and reverse micelles. Reverse micelles and reverse microemulsions comprise formation of a discontinuous polar phase (for example, water) within a nonpolar (or low polar) continuous phase (for example, cyclohexane) in the presence of surfactants or emulsifiers. The discontinuous polar phase consists of nanosized droplets, whose dimensions vary with the polar phase to surfactant molar ratio. A soluble copper (II) compound is dissolved in the polar phase. Its reduction leads to formation of nanosized copper (I) compounds and/or nanosized copper metal. Copper (I) oxide, with 5 to 10 nanometer particles was prepared in this way by Zou et al., Chinese Science Bulletin, 39, (1994), pp. 14–18. Lisiecki et al., J. Physical Chemistry, 100, (1996), pp. 4160–4166, disclosed the control of copper particle size and dispersity by controlling the water/surfactant molar ratio. Nanoparticles 2 to 10 nanometers were obtained at molar ratios 1 to 10. Qi et al., J. Colloid and Interface Science, 186, (1997), pp. 498–500, also prepared 5 to 15 nanometer copper particles in reverse micelles.
Lyons et al., J. Physical Chemistry, 95, (1991), pp. 1098–1105, prepared 350 nanometer copper particles in poly(2-vinylpyridine) by the thermal decomposition and reduction of the polymer-copper (II) formate complex. Reduction of copper (II) acetate to micron and nanosized sized particles by hydrazine in the presence of poly(vinyl-2-pyrrolidone) and acetonitrile was disclosed by Curtis et al., Angewandte Chemie, International Edition in English, 27, (1988), pp. 1530–33. Hirai et al., Bulletin Chemical Society Japan, 59, (1986), pp. 367–372, obtained copper particles in the 500 to 1500 nanometer range by reducing copper (II) salts with sodium tetrahydroborate or hydrazine in aqueous solutions of water soluble polymers. McFadyen et al., J. Colloid Interface Science, 44, (1973), pp. 95–106, and Matijevic et al., Powder Technology, 63, (1990), pp. 265–75, reported formation of 300 to 1,600 nanometer copper oxide particles by reduction of copper tartrate with glucose in polymer-free aqueous systems.
Aside from the use of ultrasonic energy by Dhas, et al. mentioned above, these prior art disclosures have all used conventional conductive or convective heating, where necessary, to effect the synthesis of nanosized metals and metal oxides. Microwave assisted synthesis of nanosized oxides in polar solvents such as ethylene glycol was disclosed by Palchik, et al., J. Materials Chem., 10 (2000) pp. 1251–1254). Baghurst, et al., Microwave-Enhanced Chemistry, Kingston, H. M. and Haswell, S. J. (Editors), American Chemical Society, Washington D. C., (1997), pp. 523–550, and Rao, et al., Chemistry of Materials, 11 (1999) pp. 882–895, have published reviews of microwave-assisted inorganic reactions, but nanosized metals and metal oxides were not emphasized.
U.S. Pat. No. 4,539,041 to Figlarz et al. which issued on Sep. 3, 1985, claims the reduction of salts, oxides, and hydroxides in polyols under reflux conditions to produce micron-sized metals and oxides (see also Figlarz, M. et al., J. Materials Chemistry, 3, (1996), pp. 627–32). These references show that the process occurs via the following steps: progressive or total dissolution of the oxidized metal precursor, reduction of the dissolved species by the polyol and nucleation and growth of metal particles.
U.S. Pat. No. 5,759,230 to Chow et al. which issued on Jun. 2, 1998, claims a method of forming nanocrystalline metallic powders in the 1 to 100 nanometer range by decomposing salts, oxides, and hydroxides in refluxing polyols. The precursor compounds must be substantially soluble in the reaction mixture for nanosized particles to be obtained.
These prior art procedures have all used solid state reactions or require solubilization in polar liquids such as water, acetonitrile, or polyols to produce nanosized copper and nanosized copper compounds by chemical methods. In some cases, the average size of the copper and copper oxide particles was considerably larger than the generally recognized 100 nanometer limit for nanosized particulates.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for making nanosized metal compounds which overcome the deficiencies of the prior art methods, and the nanosized metal compounds prepared therefrom.
It is another object of the present invention to provide a method of making nanosized metal compounds which may have utility as catalysts and pigments without a need for solubilization of the metal precursors, and the nanosized metal compounds prepared therefrom.
A further object of the invention is to provide a method of making nanosized copper and copper compounds which may have utility as catalysts and pigments.
It is yet another object of the present invention to provide nanosized copper and copper oxides having an average particle size of less than 1000 nanometer.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.